Experimental Investigation on the Mechanical Instability of Superelastic NiTi Shape Memory Alloy

In this paper, primary attention is paid to the mechanical instability of superelastic NiTi shape memory alloy (SMA) during localized forward transformation at different temperatures. By inhibiting the localized phase transformation, we can obtain the up-down-up mechanical response of NiTi SMA, which is closely related to the intrinsic material softening during localized martensitic transformation. Furthermore, the material parameters of the up-down-up stress-strain curve are extracted, in such a way that this database can be utilized for simulation and validation of the theoretical analysis. It is found that during forward transformation, the upper yield stress, lower yield stress, Maxwell stress, and nucleation stress of NiTi SMA exhibit linear dependence on temperature. The relation between nucleation stress and temperature can be explained by the famous Clausius-Clapeyron equation, while the relation between upper/lower yield stress and temperature lacks theoretical study, which needs further investigation.     

超弹性TiNi形状记忆合金棒材力学行为

基于工程振动控制的角度,通过TiNi形状记忆合金棒材在室温条件下的力学性能试验,以相变应力、变形模量、残余应变、耗能能力等作为该合金棒材的力学特征参数,分析了这些特征参数随加载速率、应变幅值、载荷循环等加载工况的变化规律.结果表明:超弹性TiNi形状记忆合金棒材具有良好的耗能能力及阻尼性能,可满足工程结构振动控制的需要.但在工程应用时,应考虑加载速率、应变幅值、载荷循环等因素对TiNi形状记忆合金棒材力学行为的影响,根据具体工况合理设计.     

Embedding of Superelastic SMA Wires into Composite Structures: Evaluation of Impact Properties

Shape memory alloy (SMA) represents the most versatile way to realize smart materials with sensing, controlling, and actuating functions. Due to their unique mechanical and thermodynamic properties and to the possibility to obtain SMA wires with very small diameters, they are used as smart components embedded into the conventional resins or composites, obtaining active abilities, tunable properties, self-healing properties, and damping capacity. Moreover, superelastic SMAs are used to increase the impact resistance properties of composite materials. In this study, the influence of the integration of thin superelastic wires to suppress propagating damage of composite structures has been investigated. Superelastic SMAs have very high strain to failure and recoverable elastic strain, due to a stress-induced martensitic phase transition creating a plateau region in the stress-strain curve. NiTi superelastic wires (A _f = ?15 °C fully annealed) of 0.10 mm in diameter have been produced and characterized by SAES Getters. The straight annealed wire shows the typical flag stress-strain behavior. The measured loading plateau is about 450 MPa at ambient temperature with a recoverable elastic strain of more than 6%. For these reasons superelastic SMA fibers can absorb much more strain energy than other fibers before their failure, partly with a constant stress level. In this paper, the improvement of composite laminates impact properties by embedding SMA wires is evaluated and indications for design and manufacturing of SMA composites with high-impact properties are also given.     

冷变形对NiTiCr形状记忆合金超弹性的影响

通过测量NiTiCr形状记忆合金丝的恢复率和做拉伸实验来观察冷变形对其超弹性的影响.结果表明,不同的冷变形量对NiTiCr的超弹性有着显著的影响.当冷变形量超过27%时,NiTiCr丝的弹性随变形量的增加而显著增强,在变形量达到33%之后,弹性随变形量的变化不大.单纯的冷变形不能使NiTiCr丝呈现完全的非线性超弹性.同时讨论了实验弯曲次数与弹性稳定性之间的关系.     

热变形对TiNi形状记忆合金丝材力学性能以及超弹性的影响

通过拉伸测试Ф0．61mmTi-50．8at％Ni合金丝材退火后热拉拔过程中不同直径丝材的力学性能和弹性性能，研究了热变形对TiNi形状记忆合金丝材力学性能及超弹性的影响规律。结果表明，经过650℃退火后Ti-50．8at％Ni合金丝材超弹性较差，而断裂伸长率达50％以上。随着热拉拔变形量增大，超弹性逐渐提高，而塑性迅速降低，当热拉拔总热变形量达50％时，丝材可以获得优良的超弹性能，△σ值（Rell-ReL）为200-250MPa，残余应变小于0．1％。同时伸长率大于10％。     

热型连铸CuAlNi形状记忆合金线材的组织与力学性能

在自制的热型连铸设备上,制备出了直径为2.6mm的CuAlNi形状记忆合金线材.并对线材的组织和力学性能进行了研究.结果表明:连铸速度对CuAlNi合金线材的组织和性能有决定性影响.当铸型温度为1100～1150℃、连铸速度为75 mm/min、冷却距离为15mm、冷却水量为60 L/h时,可制备出表面质量良好的CuAlNi形状记忆合金线材.热型连铸技术制备的CuAlNi形状记忆合金线材的抗拉强度为288MPa,断后伸长率为9.43％.     

Continuous Rotary Motor Actuated by Multiple Segments of Shape Memory Alloy Wires

An attempt has been made in this study to develop a continuous rotary motor actuated by multiple segments of shape memory alloy wires (SMA motor). In order to meet the requirements of continuous rotation, large output torque, and stall torque, a unidirectional rotary actuator was designed, and five rotary actuators were fixed on one shaft in series. When every actuator is actuated in turn, the SMA motor can realize a continuous rotation. In order to simulate the rotation angle, output torque, and the actuation performance degradation of the SMA motor, Lagoudas’s constitutive model was modified to consider the cyclic actuation influence. After design and simulation, a prototype of the SMA motor was fabricated and experimentally tested to verify the feasibility and performance of the proposed design decision. The test results indicate that the SMA motor can realize continuous rotation. The rotation speed is 0.28 r/min, and the torque is 1008 N mm.     

TiNi形状记忆合金动态力学性能测试

随着TiNi形状记忆合金的开发和应用,其力学性能越来越受到重视。为了研究TiNi合金的力学性能,利用MTS万能试验机测试得到了TiNi合金不同温度下静态拉伸应力应力应变曲线,并对曲线进行了详细的分析;利用分离式霍普金森压杆(简称SHPB)对TiNi合金进行了多种高应变率下的动态压缩实验,得到了相应的应力应变曲线;利用改进的SHPB测试系统对TiNi合金进行了动态三点弯曲实验,得到了TiNi合金的动态断裂韧度。研究结果表明,TiNi合金不同于一般的金属,它的静、动态应力应变曲线出现了两个屈服平台、两个弹性阶段和两个非弹性变形阶段,同时,TiNi合金是一种比较脆的金属,在动态冲击载荷下容易发生脆断。     

Simulation of Payload Vibration Protection by Shape Memory Alloy Parts

A system of vibroisolation under consideration consists of a payload connected to a vibrating housing by plane shape memory alloy (SMA) slotted elements. The calculation of the mechanical behavior of the SMA is based on a microstructural theory. Simulations of harmonic and of impact excitations are carried out. The results have shown that protective properties of this system depend on the SMA state. The maximum reduction of the acceleration amplitude for harmonic excitation is reached when the SMA is in the martensitic (pseudo-plastic) state or in the two-phase state. A variation of temperature allows changing the resonance frequency and thus escaping from the resonance and controlling a mode of vibration.     

An Examination of the Mechanical Behavior of Shape Memory Nitinol Wires at Various Temperatures

Shape memory Nitinol alloys are commonly used in a myriad of strain recovery applications. Understanding the behavior of the material at different temperatures influences the choices of the application designer when selecting different grades of Nitinol. This study focuses on six Nitinol ingot austenitic start (A _s) temperatures (Ingot A _s = 95.0, 84.0, 62.3, 41.6, 29.3, and 13.4 °C). Each sample was drawn to wire diameters ranging from 0.076 to 1 mm, two sizes per ingot A _s, with varying heat treatments to achieve various active austenite transformation temperatures ranges (TTR). TTR behavior was measured utilizing a linear variable displacement transducer (LVDT) bend and free recovery (BFR) method, per ASTM F2082. Mechanical characterization was determined by a series of uniaxial tensile tests performed at 5, 10, 15, 20, 30, 50, 75, and 100 °C above respective active A _f transformation temperatures. This study will detail the methods utilized in determining the results and potential impact on current industry test modalities and standards.     

基于二维激光扫描的复合材料层合板热振试验装置研发与应用

研发了一套基于二维激光扫描测试装置的复合材料层合板热振试验装置.利用PLC控制器、触摸屏、滑台型导轨、步进电机、激振器、功率放大器、激光测振仪、加热及温控装置、振动控制仪及数据采集分析装置等,建立了满足层合板高温测振需求的硬件系统.基于PLC梯形图语言编写了二维激光扫描测试装置的控制软件,并详细介绍了手动、自动控制模块...     

形状记忆合金颗粒增强铝基复合材料的制备技术

介绍了CuZnAl形状记忆合金颗粒增强的铝基复合材料的制备方法——加压渗流技术及其实验装置，以及由此技术制备的复合材料的微观形貌。     

时效处理对Ni-Ti-Ta形状记忆合金性能的影响

采用真空电弧熔炼法制得式为Ni46Ti44Ta10(at％)的锭子，经过均匀化处理后，轧制成板材用作试样；采用DSC，XRD，SEM以及显微硬度测试等试验手段，对经时效处理的新型Ni-Ti-Ta形状记忆合金的性能进行了研究。结果表明：在300℃—550℃对Ni466Ti44Ta10合金进行时效处理后，有Ti11Ni14沉淀相析出，并且产生沉淀硬化效应；合金的相变温度和硬化程度随着时效处理的参数的不同而不同；经适当的时效处理，该合金不仅具有优越的形状记忆效应，而且可以达到最好的硬化效果。     

Ti-50.8Ni合金的相变、形状记忆和超弹性特性

用热重分析仪、X射线衍射仪、光学显微镜、示差扫描热分析仪和拉伸试验研究了Ti-50.8Ni形状记忆合金的组织、相变、形状记忆效应(SME)和超弹性(SE)特性。结果表明,Ti-50.8Ni合金在600℃以下退火后组织呈纤维状,在该温度以上退火后组织呈等轴状。加热温度超过600℃后合金氧化加剧。随退火温度Ta升高,合金冷却/加热过程中的相变类型由A→R→M/M→R→A型向A→R→M/M→A型再向A→R/R→A型转变(A—奥氏体,R—R相,M—马氏体),合金的M相变温度升高,R相变温度降低,M相变热滞降低,合金室温特性由SME+SE向SE转变。形变温度Td<20℃时,合金弹簧呈SME+SE,Td>30℃时,合金弹簧呈SE。随Td升高,合金弹簧的应力诱发M应力升高。     

Mechanical Properties of Laminated Aluminum-Based Plates with Gradient Interface

Two laminated composites, 2024/3003 and 7075/6009 aluminum alloys were prepared by double-stream-pouring continuous casting (DSPCC) followed by plastic deformation and heat treatment. The interface characteristics between the external and internal layers of the composites in the as-cast and plastic deformation conditions were analyzed. The results show that the macrostructure difference between the external and internal layers of both composite ingots in the as-cast condition can be clearly clarified but th...     

形状记忆合金在土木工程中的阻尼特性研究

采用真空烧结的方法制备了SiC含量分别为0%、3%和5%的土木工程用SiC/NiTi复合材料,并对三种复合材料的物相组成、显微组织和阻尼性能进行了研究。结果表明,随着复合材料中SiC含量的增加,土木工程用SiC/NiTi复合材料的密度和孔隙率都表现为逐渐降低,第二相的种类和含量逐渐增加;土木工程用SiC/NiTi复合材料的内耗值会随着SiC含量的增加而逐渐降低。     

Martensitic Transformation and Shape Memory Effect of NiCoMnSn High Temperature Shape Memory Alloy

This article studies the dependence of martensitic transformation on Mn:Sn ratio in Ni₄₃Co₇Mn_50?x Sn _x alloy and the shape memory behavior of Ni₄₃Co₇Mn₄₃Sn₇ in detail. The results show that all the transformation temperatures show a linear decrease with the decrease of Mn:Sn ratio. The similar tendency is also found in the change of T _c. Ni₄₃Co₇Mn₄₃Sn₇ alloy exhibits a moderate shape memory effect and the maximum shape recovery strain is 2.96%. Temperature memory effect is also observed in Ni₄₃Co₇Mn₄₃Sn₇ alloy.     

Improved Shape Memory Characteristics of Fe-14Mn-6Si-9Cr-5Ni Alloy Via Mechanical Alloying

In this work, the aim was to investigate how the deformation by cold rolling affects the microstructure and transformation temperatures of Fe-14Mn-6Si-9Cr-5Ni alloy prepared by powder metallurgy route. The characteristic of the martensitic transformation in the given alloy composition was investigated in terms of the amount of deformation via cold rolling. Mechanical alloying was applied for reaching better chemical homogenization level in powder state and for this purpose the as-blended powder mixture having target composition was mechanical alloyed for 4 h under protective atmosphere. Compacted samples were sintered at 1150 °C for 2 h under Ar atmosphere. After applying different amounts of cold deformation to the sintered samples, the changes in microstructure of the shape memory alloys were characterized by x-ray diffraction and scanning electron microscopy. With increasing amount of cold deformation, shape memory recovery ratios increased remarkably and ε-martensite phase was simultaneously detected during phase analysis.     

退火处理对NiTi记忆合金丝力学性能的影响

以德国Memory-Metalle有限公司生产的两种型号NiTi合金丝为研究对象,其一是具有中温激励特性的M型,其二是具有超弹性的N型,通过拉伸实验,研究了退火处理对其力学性能的影响.结果表明:不同的退火温度和退火时间对试样的形状记忆性能以及超弹性具有不同程度的影响.     

析出相形态对Ni-Ti形状记忆合金力学性能的影响

对室温奥氏体相NiTi形状记忆合金进行热处理,在300和500℃时效温度下,分别获得具有粒状和针状Ni4Ti3析出相的组织特征,对两种组织的合金进行准静态和动态力学性能研究,对比分析析出相形态对奥氏体NiTi形状记忆合金静动态力学行为的影响规律。结果表明,准静态拉伸加载下,随应变率的提高,两种组织的应力诱发马氏体相变过程均呈现明显的应变率效应,对比分析发现,针状组织的NiTi合金发生应力诱发马氏体相变的初始应力值低,材料塑性好,抗拉强度高;准静态压缩加载时,两种组织的力学性能相近;动态压缩加载时,针状组织的动态压缩屈服强度显著高于粒状组织,但是由于粒状组织马氏体塑性变形阶段表现出更强的应变硬化效应,导致二者的动态抗压强度值相近。论文对相关机理进行了讨论和分析。